cpufreq: amd-pstate: simplify cpudata pointer assignment

move the cpudata assignment to cpudata declaration which
will simplify the functions.

No functional change intended.

Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>